1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus such as a laser beam printer, a copier, and a facsimile machine, and more particularly to an image forming apparatus in which a development unit, a photoconductive unit, and the like are made attachable and detachable.
2. Description of the Related Art
In an electrophotographic image forming apparatus, image formation is basically conducted in the following order. At first, a surface of a photoconductive body is uniformly charged by a charging device, and then a laser beam is applied to the photoconductive body surface to thereby form an electrostatic latent image thereon. Subsequently, on the photoconductive body surface carrying the electrostatic latent image is attached toner which has been charged in a potential reverse to the potential of the latent image portion, thereby visualizing the electrostatic latent image. In this way, the toner deposited on the photoconductive body surface is transferred onto a recording medium such as a paper sheet.
Most of the components for use in image formation, such as the photoconductive body, the charging device, and the toner, are consumable articles. To achieve a streamlining in maintenance and care, these components are classified and unitized according to their configurations in the apparatus, functions, differences in service life, etc, to form, for example a photoconductive unit and a development unit. Some units are made attachable to and detachable from the apparatus main body. Moreover, heavily-consumed and frequently-replaced portions, such as toner of the development unit and a member for holding the toner, are formed into a cartridge structure, for example a toner cartridge, which is made attachable to and detachable from the unit main body.
Further, in a compact image forming apparatus that satisfies user's demand for saving in space, each unit and other functional components other than the units are arranged and housed within the image forming apparatus main body at high density and with high accuracy.
Usually in such a compact image forming apparatus, replacement of its constituent units and functional components has to be conducted in accordance with a predetermined attachment/detachment order because of a restriction in function or structure, for example positioning accuracy among a plurality of units. Thus, operators or users carry out replacement in accordance with the attachment/detachment order, looking at an operation manual or the like.
In cases where a plurality of units of different types are provided that are made attachable to and detachable from the image forming apparatus main body, these units must be mounted so as not to interfere with each section of the apparatus main body, with highly accurate positional relationship maintained among the units. Thus, it is imperative that each unit be attached and detached, in a predetermined order, along a predetermined attachment path, by means of a guide formed in the apparatus main body.
Taken up as one explanatory example is an image forming apparatus disclosed in Japanese Unexamined Patent Publication JP-A 62-272283 (1987). This image forming apparatus includes an image forming unit and a development device. The image forming unit is composed of a photoconductive drum, a charging device, a cleaning device, etc. On attachment of the image forming unit and the development device to the image forming apparatus main body, first comes the image forming unit, then the development device. On detachment of the image forming unit and the development device from the image forming apparatus main body, first comes the development device, then the image forming unit.
More specifically, the image forming unit is attached to the image forming apparatus main body first, and, after the development device is guided by an attachment guide which is formed integrally with the image forming unit, the attachment guide co-operates with a positioning boss which is formed in the development device, and thereby the positioning boss is fitted into a positioning hole formed in the image forming unit. As a result, the development device is accurately positioned with respect to the photoconductive body surface of the image forming unit. Moreover, the positioning boss and the positioning hole constitute retaining means. By fitting the positioning boss into the positioning hole of the image forming unit, the development device is retained in the image forming apparatus main body so as to press-support the image forming unit. In this way, the development device cannot be mounted unless the image forming unit is attached to the image forming apparatus main body. With this structure, occurrence of an error in the unit attachment order can be prevented.
Taken up as another example is an electrophotographic apparatus disclosed in Japanese Unexamined Patent Publication JP-A 5-6037 (1993). In this construction, the attachment order is that after the photoconductive unit is attached to the apparatus main body, the development unit is attached thereto. If the development unit is attached to the apparatus main body first, a regulating member provided in the apparatus main body is shifted to a regulation position to regulate the attachment of the photoconductive unit. On the other hand, the detachment order is reverse to the attachment order, that is, after the development unit is detached from the apparatus main body, the photoconductive unit is detached therefrom. In the attachment of the development unit, the regulating member remains at a regulation position to regulate the detachment of the photoconductive unit. In this way, by the action of the regulating member provided in the electrophotographic apparatus main body, occurrence of an error in the unit attachment/detachment order can be prevented.
Taken up as still another example is an image forming apparatus disclosed in Japanese Unexamined Patent Publication JP-A 10-268734 (1998). In this construction, the attachment order is that, after a photoconductive body cartridge is attached to the image forming apparatus main body, a development device cartridge is attached thereto. Note that the “cartridge” described in JP-A 10-268734 corresponds to the “unit” described in the present specification in question. A guide portion provided in the photoconductive body cartridge and a guide groove formed in the apparatus main body co-operate with each other, so that the development device cartridge is guided to the attachment position. With this structure, when an attachment worker tries to attach the development device cartridge to be attached subsequently in a state where the photoconductive body cartridge to be attached firstly remains unattached, since the development device cartridge cannot be guided by the to-be-attached-first photoconductive body cartridge, the attachment of the development device cartridge turns out to be difficult. Hereupon, the attachment worker is able to find immediately an error in the attachment order.
However, in the case of handling the above-described conventional image forming apparatuses, in reality, users do not always abide by the predetermined order in which the functional units are attached. Thus, if the units are attached forcibly in an erroneous order, the image forming apparatus suffers from damage caused by interference between the units, or interference between the unit and the other member disposed within the apparatus main body.
The image forming apparatus disclosed in JP-A 62-272283 pays no regard to safety and prevention of an error in the order in which the development device and the image forming unit are detached from the apparatus main body. That is, even though at first the means for retaining the development device is operated to release the retention to the apparatus main body and the detachment operation is carried out in a proper order, within the apparatus main body, separation between the development unit (to be detached from the apparatus main body first) and the image forming unit (to be detached therefrom subsequently) ends in imperfect. As a result, there is a possibility that the development and image-forming units are pulled out in a mutually-coupled state. This is because the positioning boss formed in the development device and the positioning hole formed in the image forming unit are tightly engaged with each other in order to secure positional accuracy between the development unit and the image forming unit. If the development and image-forming units are pulled out in a mutually-coupled state, there is a danger of them being separated and fall off at the instant when detached from the apparatus main body. Another problem is that the to-be-detached-first development unit cannot be removed smoothly from the apparatus main body.
Moreover, in cases where the functional units are so designed as to prevent an error in the attachment order, the attachment path, through which the units are guidedly directed to the attachment position, becomes inevitably complicated. For example, in the constructions disclosed in JP-A 5-6037 and JP-A 10-268734, a shutter operating mechanism is provided in the unit and the attachment path. The shutter operating mechanism acts to open and close a shutter, only when the unit is attached and detached in a proper order, by exploiting the relative movement between the unit and the other unit or the member within the apparatus main body. The shutter is disposed in the development unit as a mechanism for opening and closing a toner supply port, which is opened only when the unit is attached in a proper order, in a state where toner is provided in a predetermined development portion, but meanwhile held closed, when the unit is attached in an erroneous order or the unit is brought to a standstill partway along the attachment path, so as to stop toner supply. In this way, when attached in an erroneous order, the unit no longer functions properly, so that users become aware of the erroneous order. Hence, occurrence of an error in the attachment order can be prevented. In such a structure, however, not only the attachment path but also the unit needs to have a complicated configuration. Furthermore, in the construction disclosed in JP-A 5-6037, since the regulating member is composed of a plurality of members including a rotation transfer gear and an urging spring, the attachment path is increased in complexity.
As explained thus far, in the conventional image forming apparatuses, although errors can be prevented from occurring in the orders in which a plurality of units are attached and detached, the path for attachment of each unit becomes inevitably complicated. This gives rise to a problem that some users find it difficult to place the unit in a predetermined position of the apparatus main body properly.
In particular, if the apparatus is inadvertently activated in a state where the unit is not placed in the attachment position properly due to the interference between the unit and the member being moved along the attachment path, it is impossible to make full use of the capabilities of the apparatus, let alone each component may suffer from damage due to misregistration of the units.